These are drastically better than the first three.
I picked numero dos. I themed my concepts around an ancient city that floats above a world clouded in poison and deadly creatures. Using their ability to harness and control energy flow, they forge weapons, gadgets and technology that only their race can use. Otherwise, the weapons are just chunks of rock and metal. Their foundation is slowly crumbling and falling, and they are struggling to survive and keep their city from sinking into the poison. They use primitive weapons like spears and swords and bows, but they are powered by the energy flowing in the city and in each person, like runes. So they are pretty much aliens.
- Runes/energy flow/magic